A photovoltaic system comprises a plurality of solar cells and one or more photovoltaic inverters. Solar cells are well known devices for converting solar radiation to electrical energy. An inverter converts direct current (DC) generated by the solar cells to alternating current (AC).
Photovoltaic systems can operate at any voltage between short-circuit voltage where the voltage is zero and open-circuit voltage where the voltage is at the maximum that can be generated by the photovoltaic system. There is an associated current with each point of voltage operation. In order to maximize the output power of the photovoltaic system, the optimal current and voltage operating points must be located. The operating point where the output power of the photovoltaic system is at its maximum is known as the “maximum power point” (MPP). The voltage and current of the photovoltaic system at the MPP is the maximum power voltage (Vmp) and the maximum power current (Imp), respectively.
FIG. 1 shows a current-voltage (I-V) curve 151 of an example photovoltaic system. Superimposed on the I-V curve 151 is a corresponding power-voltage curve 152 of the photovoltaic system. At the MPP (see 153), the photovoltaic system outputs a maximum power current Imp and a maximum power voltage Vmp. The output power of the photovoltaic system at the MPP is the maximum power Pmp, which is the product of Vmp and Imp. It is to be noted that the open circuit voltage Voc occurs when the system current is zero, and the short circuit current Isc occurs when the system voltage is zero.
Photovoltaic systems perform MPP tracking to maintain their outputs at the MPP. Example methods of MMP tracking include the “perturb and observe” (P&O) method and the “incremental conductance” (IncC) method. In the P&O method, the voltage or current of the photovoltaic system is perturbed by a small step size to detect a corresponding change in power. If the power increases, the perturbing continues in the same direction; if the power decreases, the perturbing is changed to the opposite direction. As its name implies, the incremental conductance method utilizes the incremental conductance (dI/dV) of the photovoltaic system to compute the sign of the change in power with respect to voltage (dP/dV) to track the maximum power point.